This invention relates to zero leakage valves, and more particularly to zero leakage valves employing dual seats and dual poppets wherein one set relies on a metal-to-metal or hard seal and the other seat relies on a resilient or soft seal when the valve is operable by independent means even though it may function as a conventional check valve as well.
The basic valve closure components are shown and described in U.S. Pat. No. 4,172,469 entitled "Soft Seat Check Valve," issued to the same inventor and assigned to the same assignee as this application, the disclosure of which is hereby incorporated by reference.
As explained in the reference, zero leakage is achieved by employing a double seat and poppet arrangement operating in series. One seat poppet combination utilizes a resilient sealing means and the other seat poppet combination employes a metal-to-metal seal. Successful operation of the valve requires that the hard seat always closes first and opens last so that the resilient seal seat always opens and closes at essentially zero fluid flow. This feature is readily accomplished in the conventional check valve application where the downstream pressure is always slightly higher when the valve closes and the upstream pressure is slightly higher when the valve opens, and in both opening and closing the differential pressures are quite small. However, where the valve closure components are operated by an independent means, e.g. a piston, the relative pressures may be reversed and the differential pressures may be very high. When the differential pressure is high and the higher pressure is on the side of the poppet which tends to close the poppet in the conventional check valve, the reaction of opening the soft seat poppet is as shown in FIG. 3. When the soft seat poppet is forced to open, the o-ring is pulled out of its groove by the pressure that has slowly leaked across the hard seat poppet. Even though full differential pressure is seen across the soft seat poppet, it always opens and closes under essentially no flow. The resilient seal is pulled from its groove by the differential pressure which forces the seal to stay in engagement with the poppet seat and a side of the o-ring groove. Once the resilient o-ring seal is extruded from its groove, it will be damaged or lost and can no longer function as a zero leakage valve.